Thermal conductivity is highest in

Answer: Option C

The thermal conductivity of a material is a measure of its ability to conduct heat. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity.
The thermal conductivity of sand is highest in comparison to other soil particles given in the options. The thermal conductivity of dry coarse sand is 2.05 W/m/oC at steady state conditions.